XMPP server software
Ejabberd - XMPP server software. Ejaberd known to withstand high loads. Ejabbeed used by such large companies as WhatsApp, Facebook, Google, Nintedo.Code server written in Erland.There is a free and paid version of ejabberd. In the paid version, improved technical support. The paid version supports clustering better and has better performance. Ejabberd is a better solution for large servers, but more complicated for administrators. If used PostgreSQL or MariaDb updates are maintained manually.
The server software was created by Russian programmer Andrey Shchepin. Now Shchepin sold Ejabberd to a French company and resides in France
Prosody - XMPP server software. Easy for installation and upgrade. Most popular solution for small and personal XMPP servers. Write code to lua. By default uses SQLite database. Used one core for multicore processors. Able to withstand loads of several thousand users online.